1. Field of the Invention
Embodiments of the invention described herein pertain to the field of aerial cable rail systems. More particularly, these embodiments enable the movement of objects within three-dimensional space.
2. Description of the Related Art
An aerial cable rail system is a system based on an elevated cable or rope, along which objects are transported. Existing cable rail systems rely on large fixed structures and/or complex control systems in order to facilitate the movement of objects. Many of these systems are impractical or difficult to use in that such systems typically fail to satisfactorily achieve the full spectrum of platform stability, ease of control, a compact footprint, ease of transport, speed, load bearing, extensibility, maintainability and platform stability.
Objects have been supported and moved through three-dimensional space via ropes and cables for various purposes in the past. In U.S. Pat. No. 494,389 to Sherman granted in 1893, a device is described allowing for movement of a hoist through three dimensional space via a complex arrangement of cables and pulleys. A logging system is described in U.S. Pat. No. 1,782,043 to Lawson granted in 1926 employs large amounts of cable and extensive reeving in order to suspend and move logs over large distances. A similar rope crane is described in U.S. Pat. No. 3,065,861 to Cruciani granted in 1960. These systems generally employ one or more highlines which are tightly stretched and from which an object is suspended. Other patents such as U.S. Pat. No. 3,043,444 to Melton granted in 1962 and French patent 2,318,664 to Kennedy granted in 1977 took a different approach to suspending and moving objects through three dimensional space by using one cable per support pulley per winch. The '444 and '664 patents minimize the amount of cable in the system but do not allow for simple control of the cables in the system since the speeds and lengths of each cable must change non-uniformly depending upon the path of motion of the supported object.
The cable movement systems previously mentioned were generally used to haul equipment or material. Simple cable support systems have also been used to support cameras in three-dimensional space on ropes with varying degrees of success. In U.S. Pat. No. 367,610 to Fairman granted in 1887, a balloon moved with two guy lines is described that allows a camera to take pictures from locations high above the ground. In U.S. Pat. No. 578,980 to Eddy granted in 1897, a group of cameras is hoisted on a kite string attached to a reel in order to capture panoramic photographs. In U.S. Pat. No. 894,348 to Seele granted in 1908, a camera is dropped from a balloon in a sphere in order to eliminate the undesirable pendulum effects and motion effects of wind from the resulting photograph that is exposed when a shutter string is fully extended. The '348 patent may possibly be the first patent that attempts to isolate an airborne camera from the jarring effects of the vehicle carrying the camera. In U.S. Pat. No. 1,002,897 to Brown granted in 1911, a camera is directly attached to a kite string with a timer in the form of a propeller that takes a picture after a certain period of time. In U.S. Pat. No. 1,301,967 to Parks granted in 1919, a kite string based camera is described that travels along the kite string to a preset point takes a photograph and automatically descends back down the kite string so that the kite does not have to be lowered between photos.
During the 1920's work was begun on stabilizing cameras carried in vehicles since the movement of the vehicles was limiting the quality of the photographs obtained. In U.S. Pat. No. 1,634,950 to Lucian granted in 1927, a gyro-stabilized camera mount is described that actively stabilizes a camera in the pitch and roll axes in order to keep a camera actively isolated from the undesired angular motion of the aerial, land or marine vehicle carrying the camera through three-dimensional space. Many other gyro-stabilizer patents were awarded after Lucian '950 and teach active stabilization for equipment when that equipment is supported by a moving vehicle.
In U.S. Pat. No. 4,710,819, a camera suspension system is described that utilizes a minimum of at least three cables wherein each cable has two ends with one end of each cable fixedly attached to an equipment support member and the other end of each cable fixedly attached to a winch. In between the fixedly attached endpoints lies a pulley that is used as a support for the cable to provide a vertical offset between the ground and the equipment support member. Movement is achieved by reeling the cables in and out to position the camera with motion between two points generally requiring all cables to move simultaneously at different rates.
In U.S. Pat. No. 4,625,938, a camera support system is disclosed in which a camera payload can be moved within three-dimensional space in a way that allows for active stabilization of velocity of the panning (vertical axis) of the equipment support member.
In U.S. Pat. No. 5,440,476, a cable support system is described for moving objects by extending and retracting independent ropes that correspond one-to-one with the number of winches and support pulleys supporting a central object. Even simple one axis movement requires that all ropes in the system change length in a coordinated fashion to prevent slack in the other ropes supporting the object. The '476 device cannot be operated in its best mode without a computerized control system as is true for the '938 and '819 devices previously mentioned.
In U.S. Pat. No. 6,566,834, an invention is disclosed in which a payload can be moved and angularly positioned within three-dimensional space. The invention requires a computer control system in order to calculate the change in lengths of the supports ropes in order to move the payload between two points. The invention appears to require power at the platform and locates the winches for the system on the platform, further reducing the payload capacity of the platform. Furthermore, the invention does not provide simple X, Y and Z independence for control purposes and it appears that complex sensing devices must be deployed in order to keep the cables tensioned properly.
In U.S. Pat. No. 5,585,707, an invention is disclosed in which a robot or person can be readily moved within three-dimensional space. The payload is limited and the support structure is small scale. If the structure were to be scaled up, obstacles such as goal posts or light poles would inhibit the motion of the payload through a path between two points defined within the cube, since there are numerous wires required to practice the invention. Also, the invention would not appear to allow the Z-axis to vary beneath the cube, and the size of the cube support structure to service a large volume of space would be extremely expensive to build on the scale required. Again, complex control is required to keep the tension in all of the ropes at the correct level during movement of the supported equipment.
In U.S. Pat. No. 5,568,189, an invention is disclosed for moving cameras in three-dimensional space. The problems with the '189 invention become apparent when attempting to enlarge the scale of the system. FIG. 4 clearly shows how the two parallel highline cables sag inward, when the payload is in the middle of the X, Y space. Since the invention does not use strong rails to support the Y-axis rope, the weight bearing of the invention is dependent upon the strength of the building or structure in which it is mounted and the springs in its weight bearing X-axis connectors. The motors for the various axes are mounted up in the rigging, which would require multiple extremely long power cables to traverse the volume of space along with the payload if the invention were modified for outdoor use. The power cables would total over 3 times the length of the longest axis to drive the far X-axis motor, the Y-axis motor and the Z-axis motor. Mounting heavy motors high in the rigging presents a major safety issue given that suspension lines can break. The size of the motors limits the payload that can be carried, and further limits the speed at which the payload can be carried. The invention is also fixed in size, not allowing for modular addition of X travel, or increasing the Y or Z-axis travel without mounting the structure in a bigger studio or building a bigger hanger. The system requires four ropes to move an object in three dimensions.